JAVA高级面试进阶训练营视频教程

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在做一些需要抓取网页的项目时，经常性的遇到乱码问题。最省事的做法是去需要抓取的网站看看具体是什么编码，然后采用正确的编码进行解码就OK了，不过总是一个个页面亲自去判断也不是个事儿，尤其是你需要大量抓取不同站点的页面时，比如网页爬虫类的程序，这时我们需要做一个相对比较通用的程序，进行页面编码的正确识别。

乱码问题基本上都是编码不一致导致的，比如网页编码使用的是UTF-8，你使用GB2312去读取，肯定会乱码。知道了本质问题后剩下的就是如何判断网页编码了。GBK、GB2312、UTF-8、BIG-5，一般来说遇到的中文网页编码大多是这几种，简化下就是只有 GBK和UTF-8两种，不夸张的说，现在的网站要么是GBK编码，要么是UTF-8编码，所以接下来的问题就是判断站点具体是UTF-8的还是GBK的。

那怎么判断页面具体编码呢？首先查看响应头的 Content-Type，若响应头里找不到，再去网页里查找meta头，若还是找不到，那没办法了，设置个默认编码吧，个人推荐设置成UTF-8。比如访问博客园首页http://www.cnblogs.com/，可以在响应头里看到 Content-Type: text/html; charset=utf-8，这样我们就知道博客园是采用utf-8编码，但并不是所有的网站都会在响应头Content-Type加上页面编码，比如百度的就是Content-Type: text/html，找不到charset，这时只能去网页里面找<meta http-equiv=Content-Type content="text/html;charset=utf-8">，确认网页最终编码，总结下就是下面几步

1. 1.响应头查找Content-Type中的charset，若找到了charset则跳过步骤2，3，直接进行第4步
2. 2.若步骤1得不到charset，则先读取网页内容，解析meta里面的charset得到页面编码
3. 3.若步骤2种还是没有得到页面编码，那没办法了设置默认编码为UTF-8
4. 4.使用得到的charset重新读取响应流

通过上面方法基本上能正确解析绝大多数页面，实在不能识别的只好亲自去核实下具体编码了

注意：

1. 1.现在站点几乎都启用了gzip压缩支持，所以在请求头里面加上Accept-Encoding:gzip,deflate，这样站点会返回压缩流，能显著的提高请求效率
2. 2.由于网络流不支持流查找操作，也就是只能读取一次，为了提高效率，所以这里建议将http响应流先读取到内存中，以方便进行二次解码，没有必要重新请求去重新获取响应流

下面分别给出Java和C#版的实现代码，页面底部给出了源码的git链接，有需要的童鞋请自行下载

Java实现

package com.cnblogs.lzrabbit.util;

import java.io.*;
import java.net.*;
import java.util.*;
import java.util.Map.Entry;
import java.util.regex.*;
import java.util.zip.*;

public class HttpUtil {

    public static String sendGet(String url) throws Exception {
        return send(url, "GET", null, null);
    }

    public static String sendPost(String url, String param) throws Exception {
        return send(url, "POST", param, null);
    }

    public static String send(String url, String method, String param, Map<String, String> headers) throws Exception {
        String result = null;
        HttpURLConnection conn = getConnection(url, method, param, headers);
        String charset = conn.getHeaderField("Content-Type");
        charset = detectCharset(charset);
        InputStream input = getInputStream(conn);
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        int count;
        byte[] buffer = new byte[4096];
        while ((count = input.read(buffer, 0, buffer.length)) > 0) {
            output.write(buffer, 0, count);
        }
        input.close();
        // 若已通过请求头得到charset，则不需要去html里面继续查找
        if (charset == null || charset.equals("")) {
            charset = detectCharset(output.toString());
            // 若在html里面还是未找到charset，则设置默认编码为utf-8
            if (charset == null || charset.equals("")) {
                charset = "utf-8";
            }
        }
        
        result = output.toString(charset);
        output.close();

        // result = output.toString(charset);
        // BufferedReader bufferReader = new BufferedReader(new
        // InputStreamReader(input, charset));
        // String line;
        // while ((line = bufferReader.readLine()) != null) {
        // if (result == null)
        // bufferReader.mark(1);
        // result += line;
        // }
        // bufferReader.close();

        return result;
    }

    private static String detectCharset(String input) {
        Pattern pattern = Pattern.compile("charset=\"?([\\w\\d-]+)\"?;?", Pattern.CASE_INSENSITIVE);
        if (input != null && !input.equals("")) {
            Matcher matcher = pattern.matcher(input);
            if (matcher.find()) {
                return matcher.group(1);
            }
        }
        return null;
    }

    private static InputStream getInputStream(HttpURLConnection conn) throws Exception {
        String ContentEncoding = conn.getHeaderField("Content-Encoding");
        if (ContentEncoding != null) {
            ContentEncoding = ContentEncoding.toLowerCase();
            if (ContentEncoding.indexOf("gzip") != 1)
                return new GZIPInputStream(conn.getInputStream());
            else if (ContentEncoding.indexOf("deflate") != 1)
                return new DeflaterInputStream(conn.getInputStream());
        }

        return conn.getInputStream();
    }

    static HttpURLConnection getConnection(String url, String method, String param, Map<String, String> header) throws Exception {
        HttpURLConnection conn = (HttpURLConnection) (new URL(url)).openConnection();
        conn.setRequestMethod(method);

        // 设置通用的请求属性
        conn.setRequestProperty("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
        conn.setRequestProperty("Connection", "keep-alive");
        conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Safari/537.36");
        conn.setRequestProperty("Accept-Encoding", "gzip,deflate");

        String ContentEncoding = null;
        if (header != null) {
            for (Entry<String, String> entry : header.entrySet()) {
                if (entry.getKey().equalsIgnoreCase("Content-Encoding"))
                    ContentEncoding = entry.getValue();
                conn.setRequestProperty(entry.getKey(), entry.getValue());
            }
        }

        if (method == "POST") {
            conn.setDoOutput(true);
            conn.setDoInput(true);
            if (param != null && !param.equals("")) {
                OutputStream output = conn.getOutputStream();
                if (ContentEncoding != null) {
                    if (ContentEncoding.indexOf("gzip") > 0) {
                        output=new GZIPOutputStream(output);
                    }
                    else if(ContentEncoding.indexOf("deflate") > 0) {
                        output=new DeflaterOutputStream(output);
                    }
                }
                output.write(param.getBytes());
            }
        }
        // 建立实际的连接
        conn.connect();
        return conn;
    }
}

C#实现

using System;
using System.Collections;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;
using System.IO.Compression;
using System.Collections.Generic;
using System.Collections.Specialized;

namespace CSharp.Util.Net
{
    public class HttpHelper
    {
        private static bool RemoteCertificateValidate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {
            //用户https请求
            return true; //总是接受
        }

        public static string SendPost(string url, string data)
        {
            return Send(url, "POST", data, null);
        }

        public static string SendGet(string url)
        {
            return Send(url, "GET", null, null);
        }

        public static string Send(string url, string method, string data, HttpConfig config)
        {
            if (config == null) config = new HttpConfig();
            string result;
            using (HttpWebResponse response = GetResponse(url, method, data, config))
            {
                Stream stream = response.GetResponseStream();
               
                if (!String.IsNullOrEmpty(response.ContentEncoding))
                {
                    if (response.ContentEncoding.Contains("gzip"))
                    {
                        stream = new GZipStream(stream, CompressionMode.Decompress);
                    }
                    else if (response.ContentEncoding.Contains("deflate"))
                    {
                        stream = new DeflateStream(stream, CompressionMode.Decompress);
                    }
                }
              
                byte[] bytes = null;
                using (MemoryStream ms = new MemoryStream())
                {
                    int count;
                    byte[] buffer = new byte[4096];
                    while ((count = stream.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        ms.Write(buffer, 0, count);
                    }
                    bytes = ms.ToArray();
                }

                #region 检测流编码
                Encoding encoding;

                //检测响应头是否返回了编码类型,若返回了编码类型则使用返回的编码
                //注：有时响应头没有编码类型，CharacterSet经常设置为ISO-8859-1
                if (!string.IsNullOrEmpty(response.CharacterSet) && response.CharacterSet.ToUpper() != "ISO-8859-1")
                {
                    encoding = Encoding.GetEncoding(response.CharacterSet == "utf8" ? "utf-8" : response.CharacterSet);
                }
                else
                {
                    //若没有在响应头找到编码，则去html找meta头的charset
                    result = Encoding.Default.GetString(bytes);
                    //在返回的html里使用正则匹配页面编码
                    Match match = Regex.Match(result, @"<meta.*charset=""?([\w-]+)""?.*>", RegexOptions.IgnoreCase);
                    if (match.Success)
                    {
                        encoding = Encoding.GetEncoding(match.Groups[1].Value);
                    }
                    else
                    {
                        //若html里面也找不到编码，默认使用utf-8
                        encoding = Encoding.GetEncoding(config.CharacterSet);
                    }
                }
                #endregion

                result = encoding.GetString(bytes);
            }
            return result;
        }

        private static HttpWebResponse GetResponse(string url, string method, string data, HttpConfig config)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = method;
            request.Referer = config.Referer;
            //有些页面不设置用户代理信息则会抓取不到内容
            request.UserAgent = config.UserAgent;
            request.Timeout = config.Timeout;
            request.Accept = config.Accept;
            request.Headers.Set("Accept-Encoding", config.AcceptEncoding);
            request.ContentType = config.ContentType;
            request.KeepAlive = config.KeepAlive;

            if (url.ToLower().StartsWith("https"))
            {
                //这里加入解决生产环境访问https的问题--Could not establish trust relationship for the SSL/TLS secure channel
                ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(RemoteCertificateValidate);
            }


            if (method.ToUpper() == "POST")
            {
                if (!string.IsNullOrEmpty(data))
                {
                    byte[] bytes = Encoding.UTF8.GetBytes(data);

                    if (config.GZipCompress)
                    {
                        using (MemoryStream stream = new MemoryStream())
                        {
                            using (GZipStream gZipStream = new GZipStream(stream, CompressionMode.Compress))
                            {
                                gZipStream.Write(bytes, 0, bytes.Length);
                            }
                            bytes = stream.ToArray();
                        }
                    }

                    request.ContentLength = bytes.Length;
                    request.GetRequestStream().Write(bytes, 0, bytes.Length);
                }
                else
                {
                    request.ContentLength = 0;
                }
            }

            return (HttpWebResponse)request.GetResponse();
        }      
    }

    public class HttpConfig
    {
        public string Referer { get; set; }

        /// <summary>
        /// 默认(text/html)
        /// </summary>
        public string ContentType { get; set; }

        public string Accept { get; set; }

        public string AcceptEncoding { get; set; }

        /// <summary>
        /// 超时时间(毫秒)默认100000
        /// </summary>
        public int Timeout { get; set; }

        public string UserAgent { get; set; }

        /// <summary>
        /// POST请求时，数据是否进行gzip压缩
        /// </summary>
        public bool GZipCompress { get; set; }

        public bool KeepAlive { get; set; }

        public string CharacterSet { get; set; }

        public HttpConfig()
        {
            this.Timeout = 100000;
            this.ContentType = "text/html; charset=" + Encoding.UTF8.WebName;
            this.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Safari/537.36";
            this.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
            this.AcceptEncoding = "gzip,deflate";
            this.GZipCompress = false;
            this.KeepAlive = true;
            this.CharacterSet = "UTF-8";
        }
    }
}

HttpUtil.java

HttpHelper.cs